Field of the Invention
The present invention relates to ceramic substrates, and, more particularly, to a ceramic substrate having a heat dissipating function.
Description of Related Art
With rapid growth in the electronic industry, electronic products are moving towards miniaturization, high functionality, and high operational speed. In order to extend the lifetime of electronic device, the industry focuses on the heat dissipation function. A light-emitting diode (LED) has several advantages, such as strong durability, small size, high vibration resistance, and high power efficiency, and is therefore widely used in the illuminating electronic devices.
In a conventional LED package, an LED chip is disposed on a ceramic substrate followed by the packaging process. As shown in FIG. 1A, a ceramic substrate 1 comprises: a board 10 having a first surface 10a and a second surface 10b, a plurality of electrical contact pads 11 disposed on the first surface 10a, a plurality of conductive pillars 13 disposed in the board 10 and connecting the first surface 10a and the second surface 10b to electrically connect with a first electrical contact pad 11 and a second electrical contact pad 12, and a metal heat sink 14 disposed on the second surface 10b. The heat generated by the LED chip during operation can be conducted from the board 10 to the second surface 10b and the heat sink 14.
However, in the conventional ceramic substrate 1 the coefficient of heat conductivity of the ceramic material of the board 10 is between 17-170 w/mk, which is far below that of the metal heat sink 14. Therefore, it takes much time for the heat generated by the LED chip to be conducted from the first surface 10a of the board 10 to the second surface 10b. Therefore, the LED package has poor heat dissipating efficiency, and the LED chip is easily failed.
A solution is proposed to extend the disposing area of some first electrical contact pads 11 of the ceramic substrate 1, so as to increase the metal conductivity pathways. As shown in FIG. 1B, a ceramic substrate 1′ has first electrical contact pads 11′. However, the via is small for the conductive pillar 13, with a radius of 100-200 μm, which is used for electrically connecting with the first electrical contact pads 11, 11′ and the second electrical contact pads 12. As a result, the heat conductivity function is not so obvious by using the conductive pillar, and the majority of heat generated by the LED chip must be conducted through the board 10. This leads to poor heat dissipation.
A different design of electrode according to the surface mounted device (SMD) is developed, by coupling part of the second electrical contact pads 12 with the metal heat sink 14 to form a ceramic substrate 1 with a large heat sink 14′, as shown in FIG. 1C. However, due to the small via size of the conductive pillars 13, 13′, the majority of heat still needs to be dissipated from the board 10, thereby failing to make efficient heat dissipation.
Accordingly, there is an urgent need to solve the foregoing problem of poor heat dissipation.